1. Field of the Invention
The present invention relates generally to complementary amplifier stages.
2. Description of the Related Art
The usefulness of a variety of signal conditioning systems is dependent upon accurate signal processing. For example, pipelined analog-to-digital converter systems are typically formed with converter stages that are serially connected to thereby convert successive samples of an analog input signal to corresponding digital codes at a high clock rate. In these systems, a sample-and-hold amplifier is typically the initial element that receives the analog input signal and provides the samples for subsequent conversion in the converter stages.
The accuracy of the conversion process is degraded if the sample-and-hold amplifier introduces errors into the samples. These amplifiers may be configured to operate in accordance with various amplifier classes. For example, class A amplifiers amplify over the whole of an input signal cycle. Their transistors are biased such that they are always conducting to some extent and are operated over the most linear portion of their transfer function. Even when there is no input signal, these transistors are always conducting so that power is wasted and efficiency suffers.
Class AB amplifiers often include a complementary stage in which each transistor processes a respective half of the input signal. This arrangement enhances amplifier efficiency but introduces errors because there is generally distortion introduced at the crossover junction between the signal halves.
Accordingly class AB amplifiers may be modified to a class AB structure in which each transistor is operated in a region that is only linear over a respective half of the waveform and which causes the transistor to conduct a small amount over the other half. In class AB amplifiers, the distortion at the crossover junction is substantially reduced.
Regardless of the operational class of amplifiers in a sample-and-hold amplifier, it is important to reduce errors in the sample generation process to thereby enhance the accuracy of the conversion process.